The coupling of individual plastic pipe sections, has been troublesome for many years because of the amount of time consumed in making the connection and the attendant excessive expense and labor, as well as the difficulties experienced with some type of couplings because of inaccessibility of the connector elements once the connection had been accomplished, as well as the difficulties experienced with some type of couplings because of their inherent inability to prevent uncoupling as a result of retractive forces exerted upon one or both of the connected pipe sections. Additionally, the introduction in recent years of corrugated pipe in increasingly larger sizes of 8 inches and larger, having different coupling characteristics because of correspondingly greater corrugation pitches, deeper valleys, thicker walls, and greater rigidity and inflexibility required to meet industry standards and performance specifications, has created a need for previously unnecessary and consequently unanticipated types of coupling systems, which are not taught by the prior art. Additionally, the increasing recognition and popularization of the usefulness of this pipe in more demanding and more stringent end use applications such as culverts and storm sewers, in addition to the traditional land drainage applications, has created a need for improved coupling systems of types previously unnecessary and consequently unanticipated and unknown. Outlined hereinbelow are some of the known and currently utilized types of coupling systems which are inherently unsatisfactory for use with such pipe over the current and projected future range of end use applications.
Pipe constructed as in the Maroschak U.S. Pat. No. 3,899,198 is not connectable in the larger sizes because the material will not stretch or deflect sufficiently so that the connection can be accomplished by manually forcing one end of the pipe into the connector. In other words, the laborer laying the pipe cannot exert sufficient axial pressure to effect the connection. Additionally, the Maroschak patent describes a design to perform the express function of providing for a releasable connection. This function is totally inappropriate in a coupling system intended for use over a range of end use applications including those in which non-releasable connections are highly desirable and releasable connections are unsatisfactory.
As shown below and in the Maroschak patent above, efforts have been made to design and produce separate plastic couplings in the form of separate sleeves, but these designs have proven unduly cumbersome, expensive, time-consuming and generally inadequate with the smaller pipe sizes and inappropriately designed to function properly with the larger pipe sizes and in the more demanding and more stringent end use applications, such as culverts and storm sewers. Additionally, none of such patents address the problems involved with double-walled pipe. One coupling has previously been designed as an integral part of the plastic pipe, as shown in Fouss et al U.S. Pat. No. 4,247,136, but it has several disadvantages, one of which is its inaccessability once the two ends of pipe have been secured thereby.
Another disadvantage is that the reduced diameter of this coupling constricts the inner diameter of the piping system at all coupled connections. This reduces the system flow capacity accordingly. This also introduces multiple points at which any carried solids can catch and build up and at which iron ochre deposits can grow and build up under certain conditions. Both of these conditions can restrict flow and, in extreme cases, create blockages causing the system failure. Also, since the latching elements are formed in the interior or male segments of the coupling, the fluid being conveyed in the pipe will be contaminated by fluid on the outside walls of the pipe which is retained within and around the latching elements.